The present invention relates to an information transmission system for use as, for example, a video-on-demand (VOD) delivery system for delivering program data such as of movies or the like on a real-time basis which are requested by subscribers from time to time, in response to the requests from the subscribers.
In a high-definition television broadcasting system or satellite broadcasting system, it has been customary for a subscriber to select a desired one of programs broadcast from a broadcasting station with a switch on a receiver.
One problem with the conventional process whereby the subscriber chooses from several programs broadcast from the broadcasting station is that the subscriber can enjoy only those programs transmitted by the broadcasting station. For example, if programs such as of movies or the like are available to a number of subscribers in a cable television system or the like, then the subscribers can select and see a desired program on a television display only while the program is being broadcast. This system is not convenient to the subscribers for the lack of program availability at the option of the subscribers.
There has recently been proposed a delivery system which delivers programs substantially on a real-time basis which have been requested from time to time by subscribers. If such a delivery system is implemented by a cable television system, then it becomes possible for a subscriber to select and enjoy a desired program at any desired time simply accessing the program.
A simplest arrangement for such a delivery system is composed of a plurality of playback units such as VTRs or disc recording and playback devices, a plurality of recording mediums on which programs have been recorded, and a controller for operating one of the playback units to play back one of the recording mediums when accessed by a subscriber.
In the delivery system, a number of subscribers may request a certain one of numerous programs to be delivered at the same time. In order for the delivery system to meet such demands from subscribers without delay, it is necessary that the delivery system have a maximum number of "m" playback units corresponding to the respective subscribers, and a maximum number of "n.times.m" programs where "n" is the number of different programs. If the number "m" of playback units is "1000" and the number "n" of different programs available is "10000", then the total number "n.times.m" of programs that should be ready for delivery becomes "10000000". Consequently, the delivery system is very large in scale and highly costly.